Rotary wing aircraft



Jun 17, 1952 R. HAFNER ROTARY WING AIRCRAFT 3 Sheets-Sheet l Filed July 5o.,\ 194e NQNQN June 17, 1952 v R. HAFNER ROTARY WING AIRCRAFT 5 sheets-sheet 2 Filed July 50, 1946 June 17, 1952 R, HAFNER 2,600,531

' ROTARY WING AIRCRAFT Filed July '50, 194e v s sheets-sheet a Patented June 17, 1952 UNITED STATES PATENT GFFICE ROTARY WING AIRCRAFT Raoul Hafner, Bristol, England, assigner to The Bristol Aeroplane Company Limited, Bristol, England, a British company Application `uly 30, 1946, Serial No. 687,129 In Great Britain August 17, 1945 ing rotation of the rotor may attain a high value f in which case if the force-be transmitted from the blade to the rotor hub through the bearings upon which the blade is turned to vary the pitch, the loading on the bearings is such that the pitch adjustments of the blade cannot be performed in the manner indicated. Accordingly it has heretofore been proposedto relieve the bearings of the centrifugal force by connecting each blade to the rotor hub by a tie rod or stranded cable which transmits the centrifugal force from the blade to the rotor hub. These, however, are disadvantageous in that with a tie rod the tensile strength and torsional rigidity are so inter-related that selection of appropriate values for each is not possible, and in the case of a cable the tensile loading introduces undesirable torsional stress or movement. On the other hand, the cyclic pitch-adjustments of the rotor-blades result in the creation of forces due to the mass moment of inertia of each blade about its pitch-change axis and such forces may be transmitted from the blade to the control by which the pilot adjusts the blade-pitch-this is clearly undesirable.

The present invention has for its object to provide an improved construction of tie rod for rotors of the kind referred to.

According to the present invention a tie-rod for a rotor of the kind set vforth comprises a plurality of individual members each of which is attached at one end to the rotor hub and at the other end to the rotor blade.

A tie-rod in accordance with the present invention permits either appropriate values to be selected for the tensile strength and torsional rigidity of the rod, or the selection of a torsional rigidity such that there is created (during cyclic pitch-change of the blades) forces which are adapted partly, or completely, to counteract the forces due to the mass moment of each blade about its pitch-change axis.

Preferably each tie-rod member is Wedgeshaped in cross-section and the members are helicopter,

assembled with'the tapering sides of adjacent tie-rod members in contact throughout the length of the tie-rod.

The face of the tie-rod members which forms a part of the periphery of the tie-rod is constituted at each end of the tie-rod member as part of a threaded element and the tie-rod members are relatively located on assembly to form the tie-rod so that said threaded element is completed whereby all the tie-rod members are capable of being simultaneously threaded as a unit into a member of the rotor hub and a part of the rotor blade.

If desired a rubber sheath or cover may be pro-` vided which extends over the length of the tierod between the pair of threaded elements or clips may encircle the rod.

A practical application of the present invention will now be described, by way of example, as applied to the rotor of a helicopter, the description being made with reference to the accompanying drawings whereof,

Figures la and 1b together form a side elevation partly in section, of a member by which the rotor blade is attached to the rotor hub of the Figures 2 and 3 are respectively views in the direction of arrows 2 and 3 of Figure 1,

Figure 4 is a side view showing the complete tie-rod in accordance with the present invention.

Figure 5 is a side view of a part ofthe tie-rod shown in Figure 4 and to an enlarged scale,

Figures 6 and 7 are respectively sections on the line 6-6 and 1 1 of Figure 5, and

Figure 8 is a side elevational View of a helicopter showing the improved device applied thereto and with parts broken away and parts in section.

Each blade of the helicopter rotor is supported in usual manner from the rotor hub (not shown) so as to be capable of rotation about a substantially vertical axis, that is in a generally horizontal plane. Each rotor blade is capable of vertical movements (usually referred to as apping movements) and of movements about an axis generally parallel with the axis of rotation of the rotor as a whole. The latter movements are normally referred to as drag movements. In Figure 1a the napping movements for the blade associated with the root attachment shown in this gure are performed about the axis a and the drag movements about the axis b. The blade is also capable of movement about axisc so as to vary the pitch of the blade. This action may be performed at the discretion of the pilot scas simultaneously to vary the pitch of all the blades of the rotor or it may be automatically and cyclically performed during the rotation of the rotor in any known manner,

To permit the movements of the blade about axis c the motor hub is provided with a radially extending armgenerally indicated by the-reference numeral IIJ v(one for each blade), the inner end of each blade (not shown) being secured to the part II (Figure 1b) of the arm lil. The arm` I constitutes the root attachment by which the blade is secured to the rotor hub, the radial arm being pivotally carried by a member I2 so that it is capable of drag movements about the axisb; the member I2 being itself supported by the rotor hub so that it is capable of flapping movements about axis a.

The inner extremity of the radial arm I0 carries a ball bearing I3, the inner race I4 of which is secured to a tubular member I5 which is carriedby-thememberl I2 as described above'. The out'e'rracen ofthe ball bearing vI3 supports a sleeve I6 which is disposed concentric withthemember I5? A similar arrangement is provided for-the outer extremityo'f the radialarm I0, a ballbearig- I1 `(Figure lb) being carried by the tubular member Iii-and serving tov support the sleeve I6 through` the agencyV ofthe partA II. It Vwill be obsrvdffrom'ligui'elb thatthe-part II is-perman" ntlyI "connected with the' sleeve I6 and that tf1` ttris mounted'on thebearings I3, I'I for rotationfabbutthe axisv .cer Since the blade is carried or attached to the part Il it follows that pit'c'hadjstrnents ofthe-blade ywill result in rotation ofI the sleeve IS-'in thefrrianner` indicated.

w Asprevouslystated, it is' desirable in order that the pitch adjustments of the blade be readily arid accurately controlled `that the centrifugal ladsftjwhichthe blade issubjected be not transrnttedffrom the sleeve I''to the tubular member lifthrough thebea-rings ISS' I'I land accordingly a tie-rod I8 is attached at oneend to the part I I and'at the-'other end 'to the tubular member I5. Irithis wayfthecentrifugal force of the blade is entirely transmitted :to the member I2 and hence to the rotor hub through the rod I3.

' It has' been AfoundV when 'thecentrifugal load of a rotorIbladef-v attains a certain value, that a tierodf-of (solid 'construction when possessed of the required' tensile strength has too great Va-tortional rigidity; it Iis necessary; however, that the tie-rodfibefofconsiderable torsional flexibility if the pitchlchan'gesfof 'theblade are to beperformed satisfactorily.

The present invention provides that the tierod@ I8v3 comprises" av pluralityVv of independent members, I9 each of which extends `from one-end to the-other 4ofl the i tie-rod. In cross-sectionthe tie-rodffI-is substantially circular as is'shown ln-Eiguresv and? and each-member I9 is wedgeshaped.Ak The tapering faces of adjacent members IS'ofthe tie -rod I8 are in contact throughout tneimegth..

The 'ends of 'each' member I9 are upset to increase they4 cross-sectional dimensions' thereof whilst' retaining Tits wedge shape. Figure 6 shows the members" I 9 4'upset in the manner indicated irroompar'ison With'the members I5 of Figure 7. It will vbe"a1;'p1'ecia.ted that by this upsetting operation the diameter of the tie-rod I8 is increased at each end (see Figuresjiand'). The` face of tn'upset-portion' ofmembers I8 which forms afpart offthe periphery of 'the-tief-rod' I8 is con'- stitucea as part 'or a threaded element so that ori-assembly of Vall the members ItoformVV aV 4 tie-rod, each end of the latter is provided with a screw-threaded portion 20.

The extremity of each member I9 is formed with a segment of a circular flange having a curved periphery, the flange being completed when the members I9 are assembled. A cap 2| is' provided to engage theflange and" maintain the members I9 in their assembled position. Furthermore at spaced points along the length ofthe tie-rod I8 there is provided a pair of clips 22 to `grip the members I9 and hold them together.

In assembling the-tie-rod I8 in the rotor one end thereof is screwthreaded into a split bush 22 whichv is formed integral with the tubular member I5 Whilst the other end of the rod is screwthreaded into a split bush 23 formed integral with the part II. The split bushes 22 and 23 are each provided with a yplurality of clamping screws 24 so that when the tie-rod IB-is screwed into position' as described it may be clamped `'within' the split Vbush thereby y pre-vv venting rotation oiv the rod relatively to its attachments during- `pitch changes of the blade.

It will be appreciated that 'i the member I2 carries a-pin--which is capableof rotation about axis 'b-rela'tivelytothe member, the pin constituti'ngfthedrag pin about which-'drag movements of the'blade are performed. The tie rod I8? passes through the pin and engages the inboard side-thereofso that the inboardfend of the-rod is solelyfsupported-by. the pin and is freefromthelm'ember I2. It will also be noted from Figure l 1a lthat the inboard' end of the rod llisspace'dib'y'a small amount from the lbearing assemblyaboutfwhich.the blade flaps, i. e. the bearingassembly having the axis a. Acccrdingly,` when the blade is Vmoved about the axes `dand bi'the inboard end of the lrod does not engage with*V the member I2 and complete freedom to perform saidmovements is permitted withlthearrangementdescribed. Of course, it will be appreciated that, if the drag movements become excessive; the inboard end of the rod may engage the member I2, but that this occurs only when the'rotorbladesare'operating in an abnormalv manner.

Preferablystopsare associated with theinnerextremity y'Jfthe" sleeve"II the stops co-operating. with corresponding: stops formedon the tubular member.' I5 The *arrangement is that under normalfoperating" conditions of the rotorV the pairs ofl stops Sare'not incontact'but that in the eventoffailure' or! overstrainof the tie-rod IB' thefstops 'of sleeve la will se Vsunlight into engagement with the stops of member- I5 and-as -av consequence the centrifugal forceof the blades will be'V transmitted directly toI the rotor hub individual members, ,the ends'of each of which form'part 'of cylindrical surfaces'which are comple'tedA on" vassembly ofl the'members to form `the tie-rod; said cylindrical surfaces being provided with screw threads received bythe screw Vthreaded portions ofthe hub andA blade; whereby'the indi? vidual members are attached as a unit to the hub and blade.

'2Q A`-helicopterrotor asJ claimedJ in claim l 5 characterized by the fact that the rod members are wedge-shaped in cross-section and that the tapering sides of adjacent members are in contact throughout their length.

3. A helicopter rotor as claimed in claim 2 characterized by the fact that the ends of each tie-rod member are upset so that the end portions of the assembled tie-rod are of greater diameter than the intermediate portions of the tie rod members.

4. A helicopter rotor as claimed in claim 3 characterized by the fact that clips hold the tie-rod members together to provide a unit assembly.

5. A helicopter rotor as claimed in claim 4 characterized by the fact that each end of each tie-rod member is provided with a segment of a circular flange having a curved periphery, said flanges being completed when said segments are assembled, and that a cap is provided and engages the completed flange at each end of the tie-rod to maintain the tie-rod members in their assembled position.A

RAOUL HAFNER,

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS w Number Name Date 14,210 Tufts Feb. 5, 1856 1,135,516 Frauenheim 1 Apr. 13, 1915 1,943,210 De Lavaud Jan. 9, 1930 1,970,114 Weigand Aug. 14, 1934 2,265,366 Hafner Dec. 9, 1941 2,365,357 Prewtt Dec. 19, 1944 FOREIGN PATENTS Number Country Date 385,074 Great Britain Dec. 22, 1932 332,451 Italy Nov. 29, 1935 

